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March 3, 1964 T. FLEER CONTROL SYSTEM FOR CLOTHES DRYERS Filed Oct. 7, 1960 2 Sheets-Sheet l FIG.

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T. P. FLEER CONTROL SYSTEM FOR CLOTHES DRYERS March 3, 1964 Filed Oct. 7, 1960 IN V E N'TO R THOMAS P. FLEER HIS AGENT QB A ww 0w mm N? 0.? V6 mm Vq Q w 3 om w Q 8 mm N :u

United States Patent Office 3,l23,4 i8 Patented Mar. 3, 1984 3,123,448 CGNTROL SYSTEM FfiR (ILGTEES DRYERS Thomas P. Fleer, Aifton, Mm, assignor, by mesne assignments, to White-Rodgers Company, a corporation of Missouri Filed (Pct. 7, I969, Ser. No. 61,232 9 Claims. (Cl.'3445) This invention relates to control systems for clothes dryers and particularly to a control system in whichmeans responsive to the dryer exhaust temperature is employed in a novel arrangement to: automatically modulate the output of the dryer heat-producing meansin a manner to achieve a rapid drying rate for any load or character of wet clothing under varying conditions of ambient temperature and humidity while at the same time precluding the risk of overheating or scorching the clothingyto automatically terminate operation of the heat-producing means :when the clothing has attained the desired dryness; and

to automatically efiect a cooling of the clothing subsequent to termination of operation of the heat-producing means.

This invention is an improvement of the dryer control system disclosed in an earlier copending application, Serial No. 809,281, filed April 27, 1959, by applicant and Joseph Roos.

In present conventional clothes dryers in which heated air or hot combustion gases are passed through a rotating drying drum and thereafter exhausted, considerable time is required to heat the drying drum and the wet clothing therein from room temperature to a temperature which will effect a rate of evaporation high enough to dry the load of wet clothing in what has become to be currently regarded as a reasonable time. It is characteristic in the operation of present conventional dryers when supplied with sufilcient heat at a constant rate that upon initiation of a drying cycle the temperature of the dryer exhaust increases rapidly and generally linearly until some point is reached wherein a relatively large and abrupt increase in the rate of evaporation of the moisture in the clothing occurs and effects a definite leveling off of the exhaust temperature curve. Thereafter, the exhaust temperature rises gradually during the major portion of the drying period and until the load is substantially dry, at which time it again rises abruptly until the maximum temperature to which the heat input is capable of heating the exhaust as well as the now dry clothing is reached. If the constant heat inputis increased in order to shorten the drying time, the leveling-oil of the exhaust temperature curve will-occur at a higher temperature, the drying rate during the gradual temperature rise will be higher, and the rapid temperature rise which occurs when the clothing approaches a dry condition will be more abrupt. This abrupt rise in temperature, which'occurs when the load approaches dryness, presents a problem when it is desired to automatically cut volf the heat supply by means of a temperature responsive device when the load becomes sufliciently dry. If the heat input is made high enough to dry the load in a reasonable time, the temperature rise which occurs just at the time the load has attained the desired dryness is so rapid that an overshoot occurs before the temperature device has had time to act, and this, of course, may result in overheating or even scorching the load of clothing.

In the earlier application referred to hereinbefore, this problem was solved by initiating a gradual reduction of the heat input rate substantially at the point at which the characteristic leveling off of the exhaust temperature curve normally occurs, and in continuing this gradual reduction of heat input during the major portion of the drying cycle to some predetermined minimum so as to maintain a substantially constant drying rate which would appear on the exhaust temperature curve as a relatively level plateau. Thetotal reduction in'heat input during this gradual reduction is such that only a relatively low, minimum heat input rate remains at the time when the clothing is approaching a dry condition. This arrangement clearly avoids the hazard of overheating the clothing and permtis the use of a conventionaltemperatur'e responsive device to effect the cut-off without appreciably lengthening the drying time.

While the control system set forth in the aforementioned application operates fully automatically and dependably when drying the usual run of clothing and fabrics, it has been found that the evaporation rates of some fabrics to be dried vary so widely from the usual run of fabrics under the same drying conditions that the temperature plateau established during the drying period may in some cases be raised to the point wherein it closely approaches or attains a preselected cut-off temperature suitable for usual fabrics and loads. This may occur when drying a load of heavy, multi-ply, fabric articles or deep pile, washable, throw rugs in which evaporation is so slow as to permit the exhaust temperature to reach too high a plateau during the drying period. In these instances it is necessary for the operator to manually adjust the cut-olf point upward in order to attain the desired dryness before the heat input is cut off.

In order to provide a clothes dryer control system which will achieve precisely the desired dryness of light or heavy loads of light or heavy fabrics fully automatically, applicant has devised means to vary the cut-off temperature setting of the heat responsive means with the drying plateau temperature so that a fixed differential between drying plateau temperature and cut-off temperature is maintained irrespective of variations in the plateau temperature caused by variation in the evaporation rate of the load.

In the present invention the primary object is the provision of a generally new and improved control system for clothes dryers which fully automatically achieves a highly uniform degree of dryness of fabrics of widely diiferent character when dried in different-sized loads under varying conditions of ambient temperature and humidity.

A further object is the provision of an automatic control system for clothes dryers which upon initiation of a drying cycle supplies heat to the dryer at a constant and relatively high rate until the characteristic levelingoif temperature of the dryer exhaust is approached, then gradually reduces the heat input rate to a predetermined minimum so as to substantially level the drying temperature during the major portion of the drying cycle as indicated by a substantially level portion or plateau on the exhaust temperature curve, and which automatically cuts off all heat supply upon a predetermined increase in the exhaust temperature above the plateau level on the exhaust temperature curve whatever this level may be as a result of the drying rate of the particular load and ambient temperature and humidity conditions.

A further object is to include in a control system of the above character means for automatically providing a cool-down period subsequent to cutting oil the heat supply, during which period operation of the dryer drum and blower is maintained.

More specifically, it is an object to provide means for sensing the drying temperature of a load of clothing in a clothes dryer at some intermediate point in the drying cycle when this temperature, as indicated by the dryer exhaust temperature, is rising at a relatively slow rate due to evaporation of the moisture in the load and for automatically cutting off the heat supply to the dryer when the exhaust temperature rises a predetermined amount above this intermediate point temperature.

Further objects and advantages will become apparent i when reading the following description in connection with the accompanying drawings.

In the drawings:

FIG. 1 is a schematic view of a clothes dryer control system constructed in accordance with the present invention;

FIG. 2 is a longitudinal sectional view of the fuel supply control device for the dryer heating means;

FIG. 3 is a part sectional view of the fuel supply control device shown in FIG. 2, showing the fuel supply cutoff mechanism in a different operating position; and

FIGS. 4 and 5 are cross-sectional views taken on lines 4-4- and 55, respectively, of FIG. 3.

Referring to FIG. 1 of the drawings, the numeral 1 generally indicates a gas-fired clothes dryer having a clothing drum 12 mounted for rotation on a shaft 14 and rollers 15, a heat producing means in the form of a burner 16, and an air circulating blower 18. Heated air and the products of combustion from burner 16 are drawn into clothing drum 12 at one point, through the drum and out of the drum at another point, then outwardly of the dryer casing through an exhaust passage 20 by the circulator 18, as indicated by directional arrows. The rear wall 22 of the drum is suitably perforated to permit free circulation therethrough. The drum 12 and circulating device 1% are provided with suitable pulleys 24 and 26 and are driven through a suitable belt or belts (not shown) by an electric motor graphically illustrated at 28.

Fuel is supplied to the burner 16 from a suitable source through fuel supply line 29, and the flow of fuel to the burner is controlled by a fuel flow device generally indicated at 30. The fuel control device 3t), shown in detail in FIG. 2, consists of a body member 32 having an inlet passage 34, an outlet passage 36, and a connecting passage 38. A partition 49 separating inlet passage 34 from connecting passage 33 is provided with a port therethrough fitted with an annular valve seat 42. A reciprocating poppet valve 44 cooperates with seat 42 to control the flow of fuel from the supply line to passage 38. The valve 44, which will be referred to as the cut-off valve, is normally biased in a closed position by a spring 46 and is moved to a full open position by a solenoid, generally indicated at 43, when it is energized. The solenoid actuator 48 includes a plunger guide sleeve 49, a slidably mounted plunger 50 to which valve 44 is attached, a plunger stop member 53 of magnetic material, and a winding 52. The solenoid 48 is suitably attached to valve body member 32.

The outlet passage 36 is formed in a hollow plug 54 threadedly engaged in a threaded opening 56 in the body member 32. Hollow plug 54 is provided with a sleeve portion 58 at the left end thereof which extends into connecting passage 38 and slidably receives a slide valve member 6t). The sleeve portion 58 of hollow plug 54 is provided with longitudinal slots 62 in the wall thereof, extending inwardly from its left end, with which slide valve 66 cooperates to vary the flow of fuel from connecting passage 38 to the outlet passage 36. The slide valve 6% is biased outwardly with respect to sleeve portion 58 by a spring 64.

A second hollow plug 66 threadedly received in the threaded passage 56 has a sleeve portion 6h extending exteriorly of the body member 32 and forming a fuel conduit leading from the body member to the base of burner 16. The outer end of sleeve portion 68 is internally threaded and fitted with a threaded orifice plug 76 having a calibrated orifice therein. The burner 16 is mounted on the body member 32 by means of mounting brackets 72 and screws 74.

A bore 73 extending from passageway 3t; and a tube 75 leading to the base of burner 16 at a point adjacent orifice plug 7!) provide a fuel passage which permits a predetermined minimum flow of fuel to burner 16 when slide valve is in its innermost position so as to cut off all fuel flow through slots 62 in sleeve 53. The tube 75 is provided at its outer end with a second orifice member '77 having a calibrated orifice therein. The purpose of providing a separate fuel passage 7375 leading from passage 33 to the burner base with a separate fuel metering orifice at the end thereof to supply the minimum flow to the burner, in lieu of merely providing a small hole or groove in slide valve 69 or in sleeve 58 for this purpose, is to maintain a substantially constant velocity of flow through the metering orifice which is passing the minimum flow. It will be appreciated that as the slide valve 6 is moved inwardly to reduce communication between passage 38 and outlet passage 36, the pressure drop in passage 36 and, therefore, the reduction in head pressure on the orifice 70 will be considerable and the velocity through the orifice in plug '70 will consequently be reduced considerably.

The turn-down or throttling limit at which a gas burner of the type shown will operate satisfactorily is considerably reduced if, at the same time the flow is being reduced, the velocity through the burner orifice is also reduced. This is so because as the throttling progresses, the fuel stream through the orfiice reaches a point wherein its kinetic energy becomes insufficient to aspirate adequtae primary air for combustion and carry it mixed therewith at sufficient speed through the burner tube to the burner head where combustion is intended to occur. When the mixture velocity drops below the speed of flame propagation, the combustion flame retreats from the burner head back to the fuel orifice where it burns entirely on secondary air. It will be appreciated, therefore, from the foregoing that the provision of the auxiliary fuel passage 7375 and the auxiliary orifice in plug 77 plays an important role in rendering applicants device more universally adaptable with respect to burner design.

Mounted on a wall of connecting passage 38 is an expansible chamber, generally indicated at 76, comprising a flexible inner wall or diaphragm 78 and a rigid outer wall 8%. A bulb 82 mounted in a position so as to be sensitive to dryer exhaust temperature communicates with a space between the flexible and rigid walls of the expansible chamber through a length of capillary tubing 84. The bulb 82, the capillary 84, and the expansible chamber form a sealed system filled with a thermally expanding liquid such as xylene. Pivotally mounted in a wall of the connecting passage $8 on a pivot 86 is a lever 88 having a long arm 99 which carries at its free end a threadedly adjustable contact member 92, the right end of which engages the outer end of slide valve 6%. The lever $8 also has a short arm 94 which is engaged at its free end by one end of a push rod 96 slidably mounted in a support member 98. The other end of push rod 96 is biased against the flexible wall 78 of the expansible chamber by a spring 1% so that, when the fluid in bulb 32 expands in response to increasing temperature, the lever 88 is rotated counterclockwise on its pivot 86 and the slide valve 60 is moved inwardly with respect to sleeve portion 58, thereby reducing the flow of fuel to the burner.

Slidably mounted in a horizontally arranged channel member m2 is a snap-action switching device 104 having an operating pin 106 which when depressed closes the switch contacts and when released permits them to open. The operating pin is arranged to engage one end of an intermediately pivoted lever 108. The lever 198 is pivotally mounted at 110 on one end of a horizontal push rod 112 which is slidably supported in a valve body cover plate 114 and engages at its other end the adjustable contact member 92 carried by the long arm of lever 88. The other end of lever It)? is arranged to alternately engage fixed stop 116 and opposed, threadedly-adjustable stop 118, which stops are carried by a vertically arranged support bracket 1Z0 rigidly attached to and movable with the slidably mounted switch 184. The switch 1th:- is biased toward the right in its guide channel 1*92 by a relatively strong spring i22with respect to'FlGS. 2 and 3, and the upper end of lever N8 is biased toward fixed stop 116 by a somewhat lighter spring 124. The spring 64 acting through the slide valve 60 and adjustable contact member 92 to return lever 38 in a clockwise direction when the expansible chamber contracts is sufiiciently strong to compress the spring 122 and move slidably mounted switch 164 leftward under these conditions. Pressure of spring 122 normally urges the switch operating pin 1% against lever 1% with sufiicient force to maintain the switch 104 in a closed contact position.

Pivotally supported at the upper open side of guide channel 102 on a pivot 125 supported in brackets 126 is a detent 128 having a portion 13% thereof adapted to engage the upper exposed surface of switch 194 when the detent is rotated in a counterclockwise direction. The pivoted detent 123 also has an extension 132 thereof which is operatively connected to the plunger 134 of a solenoid actuator 136 through a connecting link 133. The solenoid actuator is supported on a bracket 1.45) in fixed relationship with guide channel 192 and valve body 32. A solenoid return spring 142 normally biases the detent 123 in a position of non-engagement with slidable switch 1494 when the solenoid is tie-energized (as indicated in FIG. 2), but when the solenoid 13 6 is energized, the detent 12% is rotated counterclockwise into engagement with switch ltl i (as indicated in FIG. 3) so as to press the switch against the bottom of its channel with sufiicient force to hold it in a fixed position against the force of spring 122. The switch m4 is indicated as having a rectangular casing slidably fitting the guide channel H92, the switch casing being sufliciently rigid to withstand the pres: sure exerted by the detent 128 without distortion. Mounted on an insulating block 144 attached to the body member 32 is a pair of spaced stationary electrical contact members 146 and 1 58 which are alternately engaged by a movable contact 11% carried on the extension 132 of detent 123. When solenoid actuator 136 is ale-energized contacts 150 and 146 are biased closed, and when the solenoid is energized, contacts 150 and 146 are separated and contacts 150 and 143 are closed.

When switch ltldis held in a fixed position in its slide M2 by detent 128, a counterclockwise movement of arm 83 due to expansion of fluid in bulb 82 permits push rod 112 to be moved toward the right under the urging of spring 124*, and inasmuch as switch operating pin 1% is bottomed, the lever 1438 will rotate clockwise into engagement with fixed stop 115. Further movement of push rod 112 toward the right after lever lild has contacted stop 116 now permits switch operating pin 1% to move toward the right and thereby actuate switch Elle to an open position. The purpose of interposing lever 1% between push rod 112 and switch operating pin res is to provide means for adjustably varying the temperature change required to operate switch the after it has been locked in a fixed position by detent 125i. Movement of adjustable stop screw 11% to the left increases the temperature change required to actuate the switch, and movement of screw lllld toward the right, so as to reduce the gap between stops 118 and lid, reduces the temperature change required. k

The electrical circuitry of the system shown in FIG. 1 includes as primary elements: a pair of terminals 152 154 for connection with a suitable source of electrical power, a spring-returned, push-button switch 156, electric motor 28, the switch 104, the winding 52 of solenoid actuator 33, the winding of detent operating solenoid 136, a normally open switch 158 operated by solenoid 4-3, the double-throw switch having contacts li5-l5ll148 operated by solenoid 136, a snap-action, thermal, time switch generally indicated at 169, a current limiting resistor 172 and a line switch 174. The thermal time switch 165? comprises a bimetal switch arm 162, a resistance heater 164 for heating the bimetal, a pair of contacts 165 and 168, and a permanent magnet 17.0. The bimetal lamination FIG. 2.

will be closed and the slide valve 60 will be in its '6 having the highest coefficient of expansion is on that side which effects the closing of contacts 1dd-ll63 when the bimetal arm 1-32 is heated by resistance heater 164.

When line switch 174 is closed andpush button 156 is depressed, a circuit effecting energization of winding 52 of solenoid actuator 43 is completed. This circuit extends from terminal 15?; through a lead 176, switch 174, a lead 173, a lead 18%, push-button switch 156, a lead 182, the solenoid winding 52, and a lead 184 to terminal i5 1. Energization of solenoid winding 52 etfects opening of fuel valve 44 and the closing of switch 158, which is operatively connected to the solenoid. The closing of switch 158 completes a holding circuit for solenoid winding 52, thereby to maintain energization thereof after the starting push button 7.56 is released. This holding circuit for winding 52 may be traced as follows: from terminal 152 through lead 176, line switch 174, lead 178, switch 158, a lead 1%, a lead 138, the switch 104, a lead 1%), resistor 172, lead 182, the winding 52, and the lead 184 to terminal 154-.

The closing of switch 15.53 also completes parallel circuits for the energization of motor 28 and the resistance heater 164. The circuit for the motor 28 may be traced as follows: from terminal 152 through lead 1'76, line switch 174, lead 178, switch T53, lead 136, closed contacts 'l -5-l5tl, a lead 192, blower motor 28, a lead 194, and lead 184 to terminal 154-. The circuit branch which includes the resistance heater 164 extends from lead 136 through a lead 3 .2 6, the resistance heater 164,a lead 198,

and lead 84 to terminal 154. When the bimetal switch arm 162 has become heated sufficiently contacts 166 63 close, thereby to complete a circuit to elfect energization of solenoid 3136. This circuit may be traced as follows: from terminal 152 through lead 176, switch 174, lead 178, a lead 2%, a lead 2%2, the winding of solenoid 136, a leasea, contacts l63].66, bimetal switch arm 162, a lead 2%, and the lead 184 to terminal 154.

Energization of solenoid 136 elfects the fixing of slidable switch we and also moves switch arm so as to break with contact 146 and make with contact 148. The closin of switch contacts Hit-148 completes an alternate circuit for blower motor 28 which extends from lead 1'78 through lead 2%, contacts 14815il, a lead 392, the motor 23, and lead 19 to lead 184.

Operation When the dryer exhaust temperature to which bulb 82 is sensitive is at or below a predetermined cool-down temperature, the contacts of switch 194- will be in a closed position, as indicated in the diagram of FIG. 1, and the entire switch will be moved to a leftward position in its guide Th2 by return spring 64, as indicated in Also, under these conditions, the cut-off valve outermost position with respect to sleeve portion 58, wherein maximum fuel flow to the burner is permitted through slots 62.

Under these conditions when it is desired to dry a load of wet clothing in the dryer drum 12, the line switch 174 is closed and push button is momentarily depressed. These actions etiect energization of winding 52 of solenoid 48 through the described circuit. When energized, solenoid 48 opens valve .4 and completes the described holding circuit for its winding through the switch 158, thereby to maintain energization of solenoid 48 when the push button 156 is released. The opening of valve 44 permits fuel to flow at a maximum rate to burner 16 where it is ignited by suitable means (not shown). The closing of switch 15? also completes the described circuit for energization of motor 28 which drives the clothing drum and circulating blower, and further completes the described circuit for resistance heater 164 to start a predetermined timed period in which to effect the closing of time switch 316% and consequently, therefore, the energization of solenoid 136 through the described circuit.

Under full input burner operation, the dryer exhaust temperature will rise rapidly from room temperature until the dryer drum and the wet load therein become heated sufficiently to effect a substantial evaporation rate of moisture in the wet load and will then characteristically level off. Thereafter, if the burner were permitted to continue to operate at full capacity, the exhaust temperature would continue to rise at a considerably slower rate as the drying of the load progressed, until the load was substantially dry, and would then rise precipitously. In applicants arrangement when the exhaust temperature approaches that point at which the characteristically abrupt increase in evaporation rate effects a leveling off of the exhaust temperature curve, the expansion of the fluid in bulb $2 begins to move the slide valve an inwardly in sleeve 58 in such proportion to temperature increase as to maintain a substantially constant drying temperature which is indicated on the exhaust temperature curve as a substantially level plateau. When the slide valve 6% has moved inwardly sufficiently, fue flow through the passage 36 is cut oil? and only a predetermined minimum flow through passages 73-75 and orifice 77 will be supplied to the burner. This minimum fuel flow to the burner is in the order of 25% of the maximum flow which occurs when slide valve 6t) is in its least restricting position.

The range of burner modulation as effected by slide valve 60 and the temperature responsive actuating means is such for any particular dryer that an average wet load will be closely approaching a dry condition when the minimum fuel flow rate to the burner is reached. As the load approaches a dry condition, the exhaust temperature will begin to rise on the fixed minimum fuel flow, but the rise will be relatively gradual and the extent to which the load temperature can rise on this minimum flow is greatly reduced. By this reduction in fuel input, the response time of the temperature sensitive cut-off means is rendered considerably less critical, and the hazard of scorching the load at a time when it is approaching a dry condition is obviated.

If the load to be dried is lighter than average or if the fabric of the load is of such character that evaporation therefrom is relatively rapid, the drying time and consequently the length of the plateau of the exhaust temperature curve will be relatively short, while on the other hand if the load is heavier than average or if the fabric of the load is of such character that evaporation therefrom is relatively slow, the drying time and length of the level drying temperature plateau will be relatively long. Also, if the character of the fabric in the load is such that evaporation therefrom is relatively rapid, the plateau on the exhaust temperature curve will be lower than when drying a load of fabric from which evaporation is relatively slow. This is because the slower evaporation rate permits the exhaust temperature to rise higher at any given heat input rate. Moreover, for any size or character of load, the drying temperature plateau will be higher under operating conditions of high ambient temperature and lower under operating conditions of low ambient temperature. When the load is of a character as to be slow drying, the full range of modulation will occur earlier in the drying cycle than when the load consists of relatively rapid-drying fabrics.

Because the drying temperature or plateau temperature reflected by the temperature of the dryer exhaust varies with the load to be dried and the ambient temperature, the cut-off temperature, i.e., the dryer exhaust temperature which indicates that the load has reached a desired dry condition, must be varied to suit the load and operating conditions if the desired dry condition of the load is to be attained in all cases. This is particularly so if the desired condition of the load at the end of the drying cycle is something less than completely dry, i.e., a condition which is some degree of a so-called damp dry. The cut-off temperature can be varied manually, of course, but it would require a careful determination of the size and character of each different load and ambient operating temperature.

Applicant has discovered that by employing the sustaining drying temperature or plateau temperature as a reference point and by cutting oil heat input when the exnaust temperature rises to some predetermined point above this reference temperature, whatever it may be, a preselected dry condition of the load can be closely attained irrespective of its size, the character of fabric, or the ambient temperature. That is to say, a predetermined temperature dilferential between the sustained drying temperature or plateau temperature and a higher selected cut-off temperature will result in substantially the same degree of dryness of the load irrespective of the size or character of the load or ambient temperature.

This predetermined diferential temperature cut-oil is accomplished in the following manner: When the drying cycle is initiated, the resistance heater 164 is energized through the described circuit. After a predetermined interval contacts 166158 of thermal time switch 16% close. When this occurs solenoid 136 is energized and effects the fixing of switch 164 in its guide channel 162 at such point therein as it happens to be at the time of closing of the thermal time switch. Inasmuch as the longitudinal position of switch MP4 is a function of the exhaust temperature to which bulb S2 is sensitive and inasmuch as the push rod 112 continues to move toward the right with increasing exhaust temperature after switch 194- is fixed, it follows that switch 184 will be operated from its normally closed position to an open position by some predetermined increase in exhaust temperature above that existing at the instant the switch is fixed.

The substantially level portion or plateau of the exhaust temperature curve encompasses a considerable portion of the drying cycle, and the timing of the closing of contacts res so as to effect the fixing of switch 184 at the plateau temperature may vary within that portion of the drying cycle during which this plateau temperature is maintained. It will be appreciated, however, that the length of time which a plateau temperature will be maintained and the length of time required to attain this plateau temperature from a cold start will depend upon the size of the load to be dried and the character and moisture content of the load so that, in determining what the elapsed time should be between initiation of a drying cycle and the fixing of switch 104 to meet all conditions, these variations must be considered and a timing selected which will fix the switch at the established plateau temperature under all conditions.

After the switch 194 has been fixed, drying at the plateau temperature will continue at least until sleeve valve 66 has reached the point wherein the burner is operating at minimum capacity, and will continue beyond this point in those instances in which the load has not yet been dried to the point wherein the temperature rises appreciably at the minimum burner operation. As the exhaust temperature rises above the plateau temperature, the pivoted arm 88 continues to swing counterclockwise with push rod 112 following it toward tne right under the urging of spring 124, and the lever 1403, now fulcruming on the operating pin Hi6, swings from engagement with adg'ustable stop 118 to fixed stop 116. After the lever it)? engages stop 116, a further temperature rise causes lever 1% to now fulcrum on stop 116 and its lower end to swing counterclockwise away from switch operating pin 1%, thereby permitting switch 194- to move to an open contact position. When switch 104 opens, the circuit which energizes winding 52 of solenoid actuator is broken and valve 44 closes entirely, cutting off fuel to the burner.

When thermal time switch 160 closes effecting the energization of solenoid winding 136, normally closed contacts Eddare opened and contact 15% closes with contact 343 to establish the alternate circuit to maintain operation of motor '28 so that energization of motor 28 is then independent of switch 16401" drop-out switch 158 and is under control of thermal time switch 16%. The motor 3 and consequently thedrying drum and blower will, therefore, continue to operate after switch 164 opens to out 01f burneroperation. The opening ofswitc'h d and de-energization oi solenoid winding 52 permit dropout switch 158 to open, thereby tie-energizing resistance heating element 164. The time required for the bimetal arm 162 or" the thermal time switch to cool down and open contacts 166l63 to ole-energize motor 28 after the heater 164 is de-energized provides an automatic cooldown period during which the blower and drum are operating without heat input.

The differential temperature or'the temperature above the plateau temperature at which switch i164 opens to .cut off burner operation may be varied by manual adjustment of adjustable stop member A higher cutoff temperature is-achievedby adjusting stop 11% outward so that greater lost motionat the upper endof lever res results, and a lower cut-ofi temperature is obtained by adjusting stop 1118 inward so as to reduce this lost-motion.

The foregoing description is intended to be illustrative and not limiting, the scope of the invention being set forth in the appended claims.

I claim:

1. In a control system of the kind described, a temperature responsive device, a movablymounted control device having two opposed controlling positions and being operatively connected to said temperature responsive device, said control device being arranged to move in its entirety with said temperature responsive device as it moves in response to temperature change and thereby to remain in one controlling position irrespective of the responsive movement of said temperature responsive device, normally inoperative detent means which when operative detains said control device, thereby to eilect the relative movement therewith of said temperature responsive device upon a subsequent temperature change and the consequent actuation of said control device from one controlling position to the other, and means under the control or" a timing device for rendering said detent means operative at a predetermined time.

2. in a control system of the kind described, a temperature responsive device having a portion thereof movable in response to temperature change, a movably mounted control device having two opposed controlling positions and being normally biased in one of its controlling positions, said control device including an operating member which when pressed actuates said control device to its other controlling position, relatively strong resilient means biasing said movably mounted control device toward the movable portion of said temperature responsive device with its operating member in contact therewith, whereby said control device is moved to its other controlling position and moves in its entirety with the movable portion of said temperature responsive device, normally inoperative detent means which when operative detains said control device to permit relative movement therewith of said movable portion of said temperature responsive device, thereby to permit the return of said control device to said one controlling position as said temperature responsive device responds in one direction,'and means under control of a timing device for rendering said detent means operative at a predetermined time.

3. In a control system of the kind described, a switching device including an operating member, a temperature responsive control including an actuating member movable in response to temperature change, said switching device having a normal, returned, controlling position and an opposed controlling position to which it is moved by pressure on said operating member, said switching device being mounted for movement in the path of movement of said actuating member, resilient means biasing said switching device toward said temperature responsive device with 1% said operating member in contact with said actuating member-and with sulficient force to place said switching device in said opposed controlling position, whereby said switching device normally moves with said actuating memher and is maintained in its opposed controlling position,

normally inoperative detent means-which when operative detains said switching device thereby to permit the relative movement therewith of said actuating member in a direction away from said switching device, thereby to permit said switching device to return to its normal, returned, controlling position, and means under the control of a timing device for efiecting the operation of said detent means at a predetermined time.

4. In a control system of the kind described, a variable output heat producer, an on-oft control device having an on position in will h it permits operation or" said heat producer and having an off position in which it cuts oil? operation thereof and said control device being biased in an on position, a modulating control device operative to gradually reduce the output of said heat producer when moved in one direction, a temperature responsive device operatively connected to said modulating control device and arranged to move said device in said one direction in response to an increase in temperature above a predetermined point, a timing device, a starting control which when manually operated simultaneously initiates and thereafter maintains operation of said timing device and said heat producer so long as said on-oil? control is in an on postition, normally inoperative means which when rendered operative causes said on-oi? control device to be moved by said temperature responsive device from its 011" to off position upon a subsequent rise in temperature, and means under control of said timing device for rendering said normally inoperative means operative after a predetermined interval of operation of said heat producer.

5. in a clothes dryer having a variable output heat producer and automatic control means including a temminimum, thereby to maintain a substantially level plateau temperature as drying of the load progresses, and a cutoff control operated by the temperature responsive device to cut oi operation of the heat producer when the temperature rises above the plateau temperature; the improvement which consists in arranging the cut-off control so that it is operatively connected to said temperature responsive device but is normally tree to move in unison with responsive movements of the temperature responsive device, whereby the temperature responsive device is normally inoperative to effect operation of the cut-off control, and in providing means under the control of a timing device for stopping movement of the cut-oil control at such time following initiation of a drying cycle that this action occurs during that period of the drying cycle in which the substantially level plateau temperature exists, whereby subsequent relative movement of the temperature responsive device in response to a predetermined rise in temperature above the plateau temperature effects operation of the cut-0d control.

6. In a temperature responsive control, a temperature responsive device having an actuating member movable in response to temperature change, a switching device comprising a casing, switch contact structure in said casing and a switch operating member operatively connected to said actuating member, means mounting said switch casing for free movement with said actuating member as it moves in response to temperature change, whereby said temperature responsive device is normally inoperative to actuate said switching device in response to temperature change, normally in operative means which when rendered operative fixes said switch casing in its instant position,

1 l and a variable time delay device which after a preselected interval of operation renders said normally inoperative means operative.

7. In a temperature responsive control, a temperature responsive device including an actuating member, a control device including an operating member, means operatively connecting said operating member and said actuating member, but said entire control device being mounted for free movement with said actuating member whereby said temperature responsive device is normally inoperative to actuate said control device, time delay mechanism operative to effect the detention of said control device at a preselected time thereby to effect the relative movement of said actuating member with respect to said control device and consequently the actuation thereof upon a subsequent temperature change, and said means connecting said operating member and said actuating member including adjustable lost-motion mechanism whereby the temperature change required to eliect operation of said control device subsequent to its detention may be varied.

S. In a clothes dryer having a heat producer and means including a temperature responsive device responsive to the dryer exhaust temperature to modulate the output of the heat producer so as to maintain a substantially level drying temperature after the heat producer has operated for a sufiicient period to heat the dryer and the load to be dried to the point wherein evaporation from the load eifects a leveling off of the exhaust temperature curve, a two-position, cut-off switch being biased in an on position which permits operation of the heat producer and being movable to an off position which cuts off operation of the heat producer, means including a normally inoperative device which when rendered operative causes said temperature responsive device to operate said cutoil switch from its on to off position in response to a subsequent predetermined increase in the dryer exhaust temperature, a timing device which becomes operative after a predetermined period of operation to render said normally inoperative device operative, and starting means for simultaneously initiating operation of said heat producer and said timing device, said predetermined period of operation of said timing device being sufficient to permit the dryer exhaust temperature to attain the controlled drying temperature, whereby the cut off of heat production always occurs when the exhaust temperature rises a predetermined amount above the controlled drying temperature existing at the time said normally inoperative device is rendered operative.

9. In a control system for a clothes dryer having an electrically controlled heat producer, a rotatable drying drum, a circulating blower and duct means for passing heated air from the heat producer through the drying drum and thereafter exhausting it, and an electric motor for driving the drum and blower, a thermoelectric timing device including normally open switch contacts which close after a predetermined interval of energization of the device and reopen after a predetermined interval upon subsequent de-energization, a cut-off switch having a normal returned on position which permits operation of the heat producer, the driving motor, and said thermoelectric timer, and an off position which prevents their operation, a temperature responsive device responsive to the dryer exhaust temperature, electrically operated means which when energized causes said cut-oil switch to be operated by said temperature responsive device from its on to off position when said temperature responsive device responds to a predetermined increase in temperature, circuit means completed through said thermoelectric timing device contacts when closed for energizing said electrically operated means, means rendered operative upon the closure of said thermoelectric timing device contacts for completing a second circuit independent of said cut-off switch for maintaining energization of said driving motor when said cut-oil switch is moved to an off position, and starting switch means including drop-out holding means for initiating and maintaining operation of said heat producer, said thermoelectric timer, and said motor, so long as said cut-off switch is in an on position.

References lited in the file of this patent UNITED STATES PATENTS 2,494,925 Appelberg Jan. 17, 1950 2,654,961 Manecke Oct. 13, 1953 2,743,531 Steward May 1, 1956 2,858,618 Kaufman Nov. 4, 1958 2,878,579 Fuchs Mar. 24, 1959 2,878,580 Hughes Mar. 24, 1959 3,037,296 Cooley June 5, 1962 

1. IN A CONTROL SYSTEM OF THE KIND DESCRIBED, A TEMPERATURE RESPONSIVE DEVICE, A MOVABLY MOUNTED CONTROL DEVICE HAVING TWO OPPOSED CONTROLLING POSITION AND BEING OPERATIVELY CONNECTED TO SAID TEMPERATURE RESPONSIVE DEVICE, SAID CONTROL DEVICE BEING ARRANGED TO MOVE IN ITS ENTIRELY WITH SAID TEMPERATURE RESPONSI VE DEVIE AS IT MOVES IN RESPONSE TO TEMPERATURE CHANGE AND THEREBY TO REMAIN IN ONE CONTROLLING POSITION IRRESPECTIVE OF THE RESPONSIVE MOVEMENT OF SAID TEMPERATURE RESPONSIVE DEVICE, NORMALLY INOPERATIVE DETENT MEANS WHICH WHEN OPERATIVE DETAINS SAID CONTROL DEVICE, THEREBY TO EFFECT THE RELATIVE MOVEMENT THEREWITH OF SAID TEMPERATURE RESPONSIVE DEVICE UPON A SUBSEQUENT TEMPERATURE CHANGE AND THE CONSEQUENT ACTUATION OF SAID CONTROL DEVICE FROM ONE CONTROLLING POSITION TO THE OTHER, AND MEANS UNDER THE CONTROL OF A TIMING DEVICE FOR RENDERING SAID DETENT MEANS OPERATIVE AT A PREDETERMINED TIME. 